Spinning machines, particularly those of the type referred to as open end spinning machines, are generally provided with a central belt conveyor intended to receive the doffed bobbins and then discharge the same from the machine. Available also are devices for automatically replacing a bobbin on the bobbin carriers with a tube on which the yarn is to be wound up.
If doffing and winding tube insertion operations do not give rise to particular problems, this is not true for yarn coupling or attachment to the winding tube. Additionally, since the spinning unit continues to produce yarn during doffing operation, this requires removal of the amount of yarn produced during such an operation, which entails the necessity of cutting the yarn a first time when the bobbin has to be doffed to clear it of the yarn being produced and a second time to remove the yarn produced during bobbin doffing.
Yarn attachment or coupling to the winding tube involves problems of reliability when taking into account the very high speed at which the tube may be driven by the driving cylinder. On one hand, the tube surface state should facilitate yarn attachment, while retaining a sufficient coefficient of friction between the driving cylinder and said tube. A lapped or ground tube surface does not assure per se any yarn attachment, so that it would be difficult to ensure winding or spooling start on a new tube with a good reliability, since reliability will decrease as output rate increases.
The yarn cutting problem introduces additional complications in the device. Furthermore, these cutting operations should be strictly synchronized.